1. Field of the Invention
The present invention relates to an antenna apparatus that is suitable for use in scanning with high-frequency electromagnetic waves (high-frequency signals), such as micro waves and millimeter waves, over a predetermined angular range, and a transmitter/receiver, such as a radar and a communication apparatus, including such an antenna apparatus.
2. Description of the Related Art
In general, various kinds of beam-scanning antenna apparatuses used for an on-vehicle radar, for example, are known. For example, a first conventional technique involves the use of a reciprocal first dielectric line and a second fixed dielectric line which constitute a directional coupler, and the first dielectric line has a primary radiator connected to move with the reciprocal first dielectric line (Japanese Unexamined Patent Application Publication No. 2001-217634, for example).
Also, a second conventional technique involves the use of a reflection plate for reflecting a beam radiated from the primary radiator, which reflection plate is rotated in accordance with the beam scanning angle using a rotation mechanism, and an antenna transmitter/receiver including the primary radiator is capable of beam scanning using a cam mechanism or a link mechanism (Japanese Unexamined Patent Application Publication No. 11-27036, Japanese Unexamined Patent Application Publication No. 11-38132, for example).
Furthermore, a third conventional technique involves a dielectric disc provided in front of a transmitter/receiver antenna having thicknesses that differ with a circumferential angle, being rotated, and a hollow dielectric cylinder with an inclined axis arranged around a waveguide slot array being rotated (Japanese Unexamined Patent Application Publication No. 10-300848, Japanese Unexamined Patent Application Publication No. 6-334426, for example).
However, in the antenna apparatus according to the first conventional technique mentioned above, in addition to the necessity for a reciprocal mechanism, such as a linear motor, for reciprocating the primary radiator, etc., it is necessary to accelerate/decelerate the primary radiator, etc., along with the reciprocation of the primary radiator, so that the increased mechanical load on the reciprocal mechanism becomes a problem.
Also, in the second conventional technique, the cam mechanism and the link mechanism required for beam scanning are mechanically complicated, so that the entire antenna apparatus is liable to increase in size, and the layout of the entire antenna apparatus is complicated because of the arrangement of the cam mechanism, thereby increasing manufacturing cost.
Furthermore, in the third technique, by rotating the dielectric disc or the dielectric cylinder, the direction of a beam passing through the dielectric cylinder is changed. However, since the direction of the primary radiator is not directly changed, the dielectric cylinder tends to increase in size. Hence, there arises a problem in that the load on a motor or the like for rotating the dielectric cylinder is increased, thereby reducing reliability and durability.